Linear rheology of bituminous mastics modified with various polyolefins: a comparative study with their source binders

The effect of bituminous mastics on controlling the mechanical properties of the asphalt mixtures has been largely claimed. Theoretical models often fail to predict the rheological behavior of highly concentrated mastics because of the various interaction forces involved. This situation becomes much more complex when dealing with biphasic polymer modified bitumens (PMBs). This investigation explores the influence of various recycled polyolefins (LDPE, HDPE and PP) on the linear rheological behavior of modified mastics with a fixed filler/binder ratio of 65/35 (by weight). The filler was of siliceous-type, and all the PMBs contained 4 wt.% polymer. Oscillatory torsion/shear tests were carried out between 25 and 65 degrees C. It was found that the rheology of the HDPE-binder very much resembles its polymer-rich phase (PRP), which behaves like a concentrated polymer solution. In contrast, the LDPE-binder proved to have a bitumen-rich phase (BRP) still playing a large part in the PMB rheology. This result had a strong effect on the mastic rheology, as the filler shows more affinity for the bitumen. In consequence, the G' plateau observed in the HDPE-mastic was similar to that found in its parent PMB. In contrast, if compared to its source binder, the LDPE-mastic manifested a rheological behavior better described by the filler acting as bridging points of PRP domains.